1. Field of the Invention
The present invention generally relates to a method of forming a resist pattern, and more specifically, it relates to a method of forming a resist pattern employed for ion implantation. The present invention also relates to a method of manufacturing a semiconductor device including such a method of forming a resist pattern. The present invention further relates to an apparatus for removing an organic antireflection coating.
2. Description of the Prior Art
FIGS. 12 to 16 are sectional views of a semiconductor device showing parts of steps of a conventional method of manufacturing a semiconductor integrated circuit for illustrating a method of forming a resist pattern employed for ion implantation.
Referring to FIG. 12, a silicon substrate 102 formed with an isolation oxide film 101 is prepared.
Referring to FIG. 13, a photosensitive resist film 103 is formed on the silicon substrate 102.
Referring to FIG. 14, the photosensitive resist film 103 is first exposed to exposure light 105 such as X-rays or ultraviolet rays through a mask pattern 104.
Referring to FIG. 15, the exposed photosensitive resist film 103 is brought into contact with a developer 106 mainly composed of aqueous trimethylammonium hydride (TMAH) for removing the exposed part thereof, thereby obtaining a resist pattern 107.
Referring to FIG. 16, ions are implanted into the silicon substrate 102 through the resist pattern 107 serving as a mask.
Conventional ion implantation is performed in the aforementioned manner. However, the shape or size of the formed resist pattern 107 is disadvantageously rendered abnormal depending on the shape of the underlayer or the relative positional relation between the underlayer and the mask.
Referring to FIGS. 17A and 17B, for example, part of exposure light 202 passing through a mask 201 strikes a tapered portion on the upper end of an isolation oxide film 203 to form reflected light 205. The reflected light 205 disadvantageously exposes a part of a photosensitive resist film 206 located on an essentially unexposed region. As shown in FIG. 17B, therefore, a resist pattern 207 is formed in a shape different from a desired one. In other words, the size of the resist pattern 207 disadvantageously varies with the shape of the isolation oxide film 203.
Referring to FIGS. 18A and 18B, the isolation oxide film 203 has high transmittance for the exposure light 202. On the other hand, a silicon substrate 204 has high reflectivity with substantially no transmittance. Therefore, the exposure light 202 passing through the mask 201 is reflected by the uppermost surface and the bottom surface of the isolation oxide film 203, to form reflected light components 211 and 212. Combined light of the two reflected light components 211 and 212 sensitizes the photosensitive resist film 206. The intensity of the combined light remarkably depends on the phase shift between the two reflected light components 211 and 212. When the thickness of the isolation oxide film 203 fluctuates, therefore, the optical path length of the reflected light component 211 as well as the phase shift between the reflected light components 211 and 212 also change. Therefore, the intensity of the light exposing the photosensitive resist film 206 changes. Thus, the size of the formed resist pattern 207 also changes. In other words, the size of the resist pattern 207 disadvantageously varies with the thickness of the isolation oxide film 203.
Referring to FIGS. 19A and 19B, reflected light 221 is generated due to multiple reflection in the isolation oxide film 203 when the bottom end portion of the isolation oxide film 203 is differentially tapered. The reflected light 221 disadvantageously sensitizes a part of the photosensitive resist 206 located on the essentially unexposed region. Therefore, the resist pattern 207 is finished in a shape different from the desired one. In other words, the resist pattern 207 disadvantageously varies with the shape of the isolation oxide film 203.
In a step of forming such a resist pattern readily influenced by the underlayer, a photosensitive resist film containing a dye or an organic antireflection coating is generally employed.
The present invention is directed to a method of forming a resist pattern in an ion implantation step. A resist pattern formed according to the present invention is generally employed as a mask for implanted species, and hence the thickness of a photosensitive resist film is 2 to 6 xcexcm, which is largest among those of resist films employed in general steps of forming a semiconductor integrated circuit.
FIG. 20 shows a sectional shape of a resist pattern 303 formed from a photosensitive resist film containing a dye.
The amount of energy of light received by the photosensitive resist film from exposure light is reduced in descending order from the uppermost layer to the lowermost layer of the resist film, and hence an end of the resist pattern 303 tends to be blind over edging as shown in FIG. 20, disadvantageously leading to reduction of dimensional accuracy.
FIG. 21 shows a sectional shape of a resist pattern 404 formed through an organic antireflection coating 403. When employing the organic antireflection coating 403, influence by an underlayer can be suppressed and hence the shape of the formed resist pattern 404 is stabilized. After formation of the resist pattern 404, however, the organic antireflection coating 403 remains on the bottom of an opening 405, which must essentially be subjected to ion implantation. The organic antireflection coating 403 remaining on the bottom of the opening 405 disadvantageously serves as a mask for ion implantation.
When performing ion implantation through the organic antireflection coating 403, substances contained in the organic antireflection coating 403 are secondarily injected into a silicon substrate 401, to disadvantageously contaminate the silicon substrate 401.
In the ion implantation step for manufacturing a semiconductor integrated circuit, as hereinabove described, the quality of the underlayer for forming the resist pattern is generally optically heterogeneous as shown in each of FIGS. 12 to 21. Particularly in the device isolation step, the silicon substrate having high reflectance and the transparent isolation oxide film readily causing interference of light due to the thickness are alternately arranged while the resist pattern is formed with following the boundary between the silicon substrate region and the isolation oxide film region. Therefore, the aforementioned problems extremely readily arise. Under such circumstances, the antireflection coating is indispensable for suppressing influence by the underlayer, and a technique is required for exerting no bad influence on the silicon substrate.
The present invention has been proposed in order to solve the aforementioned problems, and an object thereof is to provide a method of forming a resist pattern, which is so improved as to exert no bad influence on a silicon substrate in ion implantation.
Another object of the present invention is to provide a method of manufacturing a semiconductor device including such a method of forming a resist pattern.
Still another object of the present invention is to provide an apparatus for removing an organic antireflection coating without exerting bad influence on a silicon substrate in ion implantation.
According to a first aspect of the present invention, a method of forming a resist pattern employed for ion implantation is provided. First, an organic antireflection coating is formed on a semiconductor substrate. A resist film is formed on the semiconductor substrate through the aforementioned organic antireflection coating. The aforementioned resist film is patterned for forming a resist pattern having an opening. A part of the aforementioned organic antireflection coating exposed on the bottom of the opening of the aforementioned resist pattern is removed.
Preferably, the part of the aforementioned organic antireflection coating is removed with ozone.
Preferably, the part of the aforementioned organic antireflection coating is removed with atomic oxygen.
Preferably, the aforementioned atomic oxygen is formed from air.
Preferably, the aforementioned atomic oxygen is formed from O2 plasma.
Preferably, the step of removing the part of the aforementioned organic antireflection coating with ozone includes steps of bringing the aforementioned semiconductor substrate into contact with ozone and heating the aforementioned semiconductor substrate thereby thermally decomposing the aforementioned ozone.
Preferably, the step of forming the aforementioned atomic oxygen from air includes steps of bringing the aforementioned semiconductor substrate into contact with air and irradiating the aforementioned semiconductor substrate with excimer light.
Preferably, the step of forming the aforementioned atomic oxygen from O2 plasma includes a step of removing charged species carrying positive charges and charged species carrying negative charges from the aforementioned O2 plasma.
In a method of manufacturing a semiconductor device according to another aspect of the present invention, an organic antireflection coating is first formed on a semiconductor substrate. A resist film is formed on the aforementioned semiconductor substrate through the aforementioned organic antireflection coating. The aforementioned resist film is patterned for forming a resist pattern having an opening. A part of the aforementioned organic antireflection coating exposed on the bottom of the opening of the aforementioned resist pattern is removed. Ions are implanted into the surface of the aforementioned semiconductor substrate through the aforementioned resist pattern.
Preferably, the part of the aforementioned organic antireflection coating is removed with ozone.
Preferably, the part of the aforementioned organic antireflection coating is removed with atomic oxygen.
Preferably, the aforementioned atomic oxygen is formed from air.
Preferably, the aforementioned atomic oxygen is formed from O2 plasma.
Preferably, the step of removing the part of the aforementioned organic antireflection coating with ozone includes steps of bringing the aforementioned semiconductor substrate into contact with ozone and heating the aforementioned semiconductor substrate thereby thermally decomposing the aforementioned ozone.
Preferably, the step of forming the aforementioned atomic oxygen from air includes steps of bringing the aforementioned semiconductor substrate into contact with air and irradiating the aforementioned semiconductor substrate with excimer light.
Preferably, the step of forming the aforementioned atomic oxygen from O2 plasma includes a step of removing charged species carrying positive charges and charged species carrying negative charges from the aforementioned O2 plasma.
According to still another aspect of the present invention, an apparatus for removing an organic antireflection coating formed on a semiconductor substrate is provided. This apparatus comprises a reaction chamber storing the semiconductor substrate formed with the organic antireflection coating. A heater for heating the aforementioned semiconductor substrate is provided in the aforementioned reaction chamber. The apparatus further comprises an ozone supplier supplying ozone into the aforementioned reaction chamber.
Preferably, the apparatus for removing an organic antireflection coating further comprises a gas shower head, provided in the aforementioned reaction chamber, having a number of gas nozzles homogeneously spouting ozone fed from the aforementioned ozone supplier toward the aforementioned semiconductor substrate.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.